The present invention pertains generally to face masks of the type worn for protection from extreme temperatures and to masks having a filtering capacity.
In the prior art are several cold weather masks which partially or fully overlie the face. Air is admitted to the nose and mouth via a filtering medium such as a nosecup as shown in U.S. Pat. No. 3,768,100 which patent states that inhaled air is "well above the ambient temperature". The filtering medium used is the well known nosecup type of molded construction with a strip of closure material applied thereto for cup securement to an underlying edge of a fabric cold weather mask. A problem exists with such masks by reason of the sizeable dead air space within the masks which results in exhaled air being again inhaled causing an increase in carbon dioxide in the body. A further drawback to the prior art masks is the complexity of same resulting in substantial manufacturing costs and cumbersome to use.
U.S. Pat. No. 4,300,240 is somewhat more relevant to the present mask in that it is formed fron one piece of resilient neoprene foam for stretched engagement with the lower face and neck. Air passes through the mask via nose and mouth openings with little or no heat transfer (countercurrent exchange) from exhaled to inhaled air. No filter unit is provided in this prior art mask.
A copending U.S. patent application filed June 1, 1982, by the present inventor, under Ser. No. 383,465, now U.S. Pat. No. 4,458,679 discloses the use of a removable countercurrent exchange medium carried in a cup-shaped face mask shell for the conservation of body heat otherwise lost by respiration.
U.S. Pat. Nos. 3,908,648 and 4,038,979 disclose masks which removably mount a filter medium in a partial or full head enclosing mask. U.S. Pat. Nos. 2,344,920 and 3,818,510 disclose face masks each having a chamber opposite the nose and mouth through which respiratory air passes but with no filtering capability.